Conventionally, in an electric stapler or the like which strikes a staple toward binding sheets to thereby bind the binding sheets together in a bundle by the staple, a U-shaped staple including a pair of leg portions extending in the same direction is struck out toward binding sheets from the front surfaces of the binding sheets by a striking mechanism, and the pair of leg portions of the staple penetrated through the binding sheets are bent or clinched along the back surfaces of the binding sheets by a clincher mechanism. For example, an ordinary clincher mechanism used in a conventional electric stapler as disclosed in JP-A-10-128683 is composed of a pair of movable clinchers which are rotatably disposed opposed to the respective staple legs penetrated through the back surface side of the binding sheets. In this clincher mechanism, after the penetration of the most portions of the staple legs of the staple struck out from a striking mechanism through the binding sheets is completed, the movable clinchers are operated and rotated to bend the staple legs along the back surfaces of the binding sheets, thereby binding the binding sheets by the staple.
The pair of movable clinchers are disposed opposed to the striking position of the staple and are rotatably supported on their respective pivots between two clincher guide plates disposed side by side in the back-and-forth direction, and the clincher surfaces of the movable clinchers are disposed so as to be engageable with the respective legs of the staple penetrated through the binding sheets. To operate and rotate the movable clinchers, there is provided a drive lever the central portion of which is rotatably supported on a frame. When the rear portion of the drive lever is engaged with a drive cam which can be rotated by a motor used to drive the stapler, the front end portion of the drive lever can be operated and oscillated in the upward and downward directions; and when the front end portion of the drive lever is engaged with part of the movable clincher and the drive lever is then operated or oscillated, the movable clincher can be rotated. When a roller mounted on the rear end of the drive lever is contacted with the cam surface of the drive cam and the drive cam is rotated, the rear end of the drive lever is operated or oscillated in the vertical direction and thus the front end portion of the drive lever is oscillated in the vertical direction about the rotation support shaft of the drive lever, thereby causing the drive lever to press down part of the movable clincher. As a result, the movable clincher is rotated about its support shaft and thus the clincher surface of the movable clincher is engaged with its associated staple leg, so that the movable clincher clinches or bends the staple leg portion along the back surfaces of the binding sheets to thereby bind together the binding sheets.
In an ordinary stapler, there are loaded staples of one kind having a leg length corresponding to the maximum thickness of binding sheets to be bound by the stapler, and these staples are used to bind binding sheets which range in thickness from the smallest to the maximum. For this reason, when binding sheets having a small thickness are bound, the length of the staple legs to be penetrated through the binding sheets to the back surface thereof is long, thereby causing the occurrence of unfavorable phenomena such as a re-penetration phenomenon in which, when the staple legs are clinched or bent by the clincher mechanism, the leading end portions of the staple legs are penetrated again through the binding sheets and are thereby projected to the front surface side thereof. As means for solving this, there is known a binding method using a so called bypass clinch in which, in order that the staple legs penetrated through the binding sheets to the back surface side thereof can be bent without interfering with each other, the side surfaces of the staple legs are bent while they are disposed so as to adjoin each other. However, in this binding method, it is necessary to form, in the clincher mechanism, a guide structure which is used to guide the staple legs in such a manner that the side surfaces of the staple legs are allowed to adjoin each other, which requires high precision of the parts of the clincher mechanism and the assembling thereof are required of high precision, resulting in the increased cost of the stapler. Further, when binding sheets with the central portions thereof staple fastened are bent half to thereby bind a book, there is required a so called in-line binding method in which the staple legs are disposed on a straight line.
Also, referring to a stapler built into a copying machine and the like, in order to prevent the staple legs from being projected out to the front surface side of the binding sheets when binding the above-mentioned thin binding sheets, there is proposed a stapler including a staple leg cutting mechanism which cuts the leading end portions of the staple legs penetrated through the binding sheet in such a manner that the staple legs projected out to the back surface side of the binding sheets can be made substantially equal in length. (For example, JP-B-02-021922). This staple leg cutting mechanism is composed of a pair of movable clinchers for bending the staple legs penetrated through the binding sheets to the back surface side thereof along the back surfaces of the binding sheets, and a fixed cutter interposed between the pair of movable clinchers, in which the leading end portions of the staple legs penetrated through the binding sheet are cut with movable cutting edges formed in the movable clinchers and fixed cutting edges formed in the fixed cutter. And, in this staple leg cutting mechanism, simultaneously when the staple legs are bent with the movable clinchers, the leading end portions of the staple legs are cut.
And, there is also proposed a staple leg cutting mechanism in which, below a movable clincher which can be engaged with staple legs penetrated through binding sheets and can bend the staple legs along the back surfaces of the binding sheets, there is provided a movable cutting member movable in a direction substantially perpendicular to the penetrating direction of the staple legs and including a first cutting edge engageable with the staple legs penetrated through the binding sheets, and, on a fixed cutting member provided so as to be able to guide the movement of the movable cutting member, there is formed a second cutting edge which cooperates with the first cutting edge of the movable cutting member in cutting the staple legs. (For example, JP-Y-03-025930). In this staple leg cutting mechanism, the staple legs penetrated through the binding sheets are engaged with the first and second cutting edges respectively formed in the movable and fixed cutting members and then the movable cutting member is moved along the fixed cutting member to thereby cut the leading end portions of the staple legs; and, after then, the staple legs are bent along the back surfaces of the binding sheets by a movable clincher mechanism.